1. Field of the Invention
The present invention relates to a wire-wound type chip coil and in particular, a small-sized wire-wound type chip coil for use, for example, in a high-frequency circuit, and also to a method of adjusting a characteristic of a wire-wound type chip coil.
2. Description of the Related Art
The structure of a conventional wire-wound type chip coil is described below with reference to FIG. 12.
FIG. 12 is a perspective view illustrating the external appearance of a wire-wound type chip coil according to a conventional technique.
In FIG. 12, reference numeral 100 denotes a chip coil, 1 denotes a core, 11 denotes flanges, 2 denotes a conductive wire, 21 denotes end portions of the conductive wire, 3 denotes terminal electrodes, and 4 denotes a coating resin.
The chip coil 100 is produced by winding one conductive wire 2 around the core 1 made of a magnetic material, and firmly connecting the two ends 21 of the conductive wire 2 to the respective terminal electrodes 3 disposed on the flanges 11 of the core 1.
The conventional wire-wound type chip coil has problems to be solved, as described below.
In recent high-frequency circuits, a very difficult process is needed to adjust the matching between a circuit element and a transmission line. To make the adjustment, it is necessary to prepare coils having a large number of different values of inductance within a small range (less than about 10 nH).
However, in conventional wire-wound type chip coils having a structure such as that described above, only integers are allowed for the number of turns of a winding connected between electrodes, and inductance is limited to corresponding values.
Specific examples of inductance values that a 1005-size (1.0 mm×0.5 mm in bottom surface size) of a wire-wound type chip coil can take are discussed below. In FIG. 11, examples of inductance values that this conventional wire-wound type chip coil can take are shown. (Note that examples of inductance values that wire-wound type chip coil according to preferred embodiments of the present invention are also shown in FIG. 11.) For example, when one conductive wire with a diameter of 50 μm is wound around a 1005-size core, only discrete inductance values such as 1.5 nH for a one-turn coil, 2.7 nH for a two-turn coil, and so on, can be obtained. Thus, values lower than 1.5 nH and values of 1.8 nH and 2.2 nH in the E12 series, and values lower than 1.5 nH and values of 1.6, 1.8, 2.0, 2.2, and 2.4 nH in the E24 series cannot be obtained.
Similarly, in a case in which a wire-wound type chip coil is formed by winding a conductive wire with a diameter of 80 μm around a 1608-size (1.6 mm×0.8 mm in bottom face size), only discrete values such as 2.2 nH for a one-turn coil, 2.7 nH for a two-turn coil, and so on can be obtained.
Thus, in this technique, available inductance is limited to special values, as long as an identical conductive wire is used. That is, in the specific example described above, inductance values lower than 2.2 nH and values between 2.2 nH and 2.7 nH cannot be obtained.